Fluorine-19 MRI at 21.1 T: enhanced spin-lattice relaxation of perfluoro-15-crown-5-ether and sensitivity as demonstrated in ex vivo murine neuroinflammation.

Objective: Fluorine MR would benefit greatly from enhancements in signal-to-noise ratio (SNR). This study examines the sensitivity gain of ¹⁹ F MR that can be practically achieved when moving from 9.4 to 21.1 T.
Materials and Methods: We studied perfluoro-15-crown-5-ether (PFCE) at both field strengths (B ₀ ), as a pure compound, in the form of nanoparticles (NP) as employed to study inflammation in vivo, as well as in inflamed tissue. Brains, lymph nodes (LNs) and spleens were obtained from mice with experimental autoimmune encephalomyelitis (EAE) that had been administered PFCE NPs. All samples were measured at both B ₀ with 2D-RARE and 2D-FLASH using ¹⁹ F volume radiofrequency resonators together. T ₁ and T ₂ of PFCE were measured at both B ₀ strengths.
Results: Compared to 9.4 T, an SNR gain of > 3 was observed for pure PFCE and > 2 for PFCE NPs at 21.1 T using 2D-FLASH. A dependency of ¹⁹ F T ₁ and T ₂ relaxation on B ₀ was demonstrated. High spatially resolved ¹⁹ F MRI of EAE brains and LNs at 21.1 T revealed signals not seen at 9.4 T.
Discussion: Enhanced SNR and T ₁ shortening indicate the potential benefit of in vivo ¹⁹ F MR at higher B ₀ to study inflammatory processes with greater detail.